Keeping the faith is sometimes the hardest thing to do.
Masello's rule #45 is primarily aimed at writers of longer works. It can literally take years to complete a book or screenplay. And during that time, you can start to have doubts about your work. He notes the importance of getting past those doubts and seeing your way through to a completed manuscript.
Although Masello doesn't say it, I believe that this same need to keep the faith also applies to those of us who concentrate on shorter works. Yes, in general there isn't as much time needed to complete a short story or even a novella, although as I've noted before, one of my novellas took me about five years to complete. (That wasn't all solid work, of course...) But when you're spending day after day pounding out short story after short story, collecting rejection slips, and hoping that one of them will eventually make it through the slush pile and into the magazine...well, it's not uncommon to become discouraged.
Of course, I do have some experience with Masello's rule when it comes to longer works as well. My first attempt to write a novel took about three years. I finished it in 2001, and it didn't sell to any publisher.
But because I kept the faith, I spent the year 2004-2005 doing nothing but writing another novel. I have no idea if that novel will ever sell, but in the meantime, among all the other writing projects and day-to-day life stuff, I've begun work on a third novel. It took me quite a few short stories before I began writing ones that sold; it's entirely possible that the same thing will be true for me when it comes to novels. But even if I never manage to publish a novel, as far as I am concerned, it will all have been worth it.
So how does one keep the faith? Masello's only real suggestion is to keep the image of the final published book in your head, and visualize yourself showing it to all your friends. I keep the faith by reminding myself that I do self-identify as a writer (among other things), and if I'm a writer, then I'd better write. But I'm curious about how other people do this, and am openly soliciting any advice people would like to share.
If you're a writer, how do you keep the faith?